WEC | Rebellion R13 | Technical Analysis

Rebellion R13 Technical Analysis

Rebellion Racing are no strangers to the WEC LMP1 privateer title, having won it from 2012 to 2016. The question is can their Rebellion R13 take them to overall LMP1 victory – beating Toyota’s hybrid TS050?

Can the privateer Rebellion R13 beat Toyota and claim the LMP1 title at Le Mans?

Engine

The Rebellion R13 is powered by the Gibson GL458 4.5L V8 engine and runs the ORECA chassis. Although this year ORECA are heavily involved in the design and running of the car as its their best opportunity to claim the overall win at Le Mans with the 2018/19 ‘Super season’ featuring two editions of the Le Mans 24 hours.

‘We wanted to run a naturally aspirated engine and decided to go with the Gibson because the external dimensions of their LMP1 engine are the same as their LMP2 engine [which they ran last year],’ highlights Bart Hayden, Team Manager at Rebellion Racing. ‘This meant that the installation was pretty straightforward because the only difference is the internals of the engine. Also, we were given the green light on this project quite late last year, so in the timescale we had, it was much easier to get this engine in than anything else.’

The Gibson LMP1 engine is a 4.5L V8 and powers both Rebellion R13 cars and Dragonspeed’s BR Engineering BR1 car

The Gibson GL458 is based on the LMP2 engine and has therefore had to increase in capacity from 4.2L to 4.5L. Consequently, this has changed the heat rejection figures and so Rebellion, along with ORECA have had to work on the cooling. ‘It needs more cooling. The car looks from outside [to be the same] philosophy as the ORECA 07, but the airflow structure is quite different, because the car in detail is different. We had to work towards improving the cooling and this has been a challenge,’ explains David Floury, Technical Director at ORECA. ‘The front of the car has quite different aero and that impacts the flow to the radiators. The flow from the front to the back is quite different and that is why in many details you see differences between the R13 and the 07.’

Aerodynamics

Luckily, ORECA were able to focus the majority of their attention on the aerodynamics of the car because of the proven concept of the Gibson engine, with their LMP2 version supplying the entire grid both this year and last. ‘Because their engine and its performance in the ORECA 07 chassis is well known, ORECA didn’t have too much guessing to do in terms of whether the figures supplied by Gibson were what you would actually see on the track,’ highlights Hayden. ‘The engine was a known quantity for them which meant that they could focus more on the aerodynamic performance of the car.’

The higher capacity Gibson engine requires more cooling and results in a different air flow structure

Like most teams, Rebellion arrived at Spa for the 1st round of the WEC series with the low downforce package to focus development on Le Mans, so there are large upgrades planned for the third round of the Championship at Silverstone in August. ‘The higher downforce elements will come post Le Mans because there is a bit of a gap between the races. The package we’ve got [for Spa] is basically the Le Mans package,’ says Hayden. ‘There is so much downforce in this car, much more than LMP2. Even in the Le Mans [low downforce] aero configuration, we’ve got more downforce than the P2 has in high downforce configuration.’

With the performance of the Gibson engine a known quantity, ORECA could invest more resources on the aerodynamic package of the Rebellion R13

Chassis

The Rebellion R13 uses the same tub as that used in both the R-One and the LMP2 customer chassis and the design is now more than five years old. However, ORECA’s late decision to take on the project compromised some of the performance upgrades that ideally would have been introduced. ‘We would have liked to have redesigned the tub, but considering the timescale to do the project from the start this was not an option,’ highlights Floury. ‘We had six months from the day we started the project to the day the car hit the track, so in this timescale we did not have time to redesign the chassis. Had we had 12 months extra for sure we would have considered it. This original chassis was designed to LMP1 2014 regulations, and it is still the monocoque regulation that is valid for LMP1 non-hybrid and LMP2.’

The short timescales meant the desired upgrades to the chassis were compromised. Courtesy of Rebellion Racing

Weight saving

Floury estimated that 10-15% weight saving could have been achieved on the Rebellion R13, however the short timescales meant that the design team had to save weight on the rest of the car instead. One of these areas was within the engine and the collaboration between ORECA and Gibson resulted in reducing the weight of the base engine unit. Another of these areas was the Xtrac gearbox which is again a similar concept as last year, but the details have been optimised to minimise weight, whilst improving efficiency.

Suspension

It’s estimated that the ACO and FIA have targeted the Rebellion R13 to achieve a 3min13s around Le Mans, which is an improvement of around 10-12s compared to last year. Naturally, this has affected everything including the weight distribution, suspension design and steering concept. The splitter, floor, and flow to the tightly regulated rear diffuser has all seen a major development too. ‘Nothing is carried over from the LMP2,’ says Floury. ‘The steering is different, the suspension geometry is different because we don’t use the same tyres, and it is not the same characteristics in terms of weight, cornering speed and so on, or in terms of engine characteristics. Weight distribution is different, and from the P2 we had to save a lot of weight, so if you keep everything the same then you don’t hit the target. We carry quite a lot of ballast in P2, but we still had a lot of weight to save for the P1. The target was not only a matter of hitting the minimum weight, but hitting the weight with ballast.’

The Rebellion R13 runs a torsion bar at the front with springs at the rear with a different geometry to the ORECA 07

Despite the different suspension geometry and uprights, the overall concept is similar to last year’s LMP2, with a torsion bar at the front and springs on the rear, running PKM dampers, which are the same as LMP2.

Brakes

Last year at Le Mans, several LMP2 teams changed their brakes during the race due to wear. ‘We knew it was marginal going into the race last year, so we wanted to make sure that in this year’s car with the increased speeds that we weren’t going to face that, so we were keen to see a good mass of carbon material in the brakes,’ explains Hayden. ‘Cooling on the brakes was a bit of a challenge in the ORECA 07 and 05, so we wanted a brake pad that was a step up in terms of cooling as well. The discs are vaned all the way through so cooling comes in through the centre of the hub and blows through the disc. We’ve got two options for the cooling and aero around the brake discs. If you’re looking for aero performance you use one and if you want to try and get heat radiated form the brakes [to the tyres] you use the other.’

The Rebellion R13 runs with AP Racing brakes and this year they feature more carbon to avoid any wear issues during the 24 hours of Le Mans

The optimum temperature at the point where the driver starts to apply the brakes is around 400°C and that temperature rises to peaks of around 800-900°C. ‘What you’re looking for is that temperature when you first hit the pedal, if it’s too cold then you don’t get the bite, if it’s too hot then you start wearing them and when they get too hot they wear very quickly,’ highlights Hayden. ‘If the brakes are working in the right window then there’s no wear at all. The drivers will lose temperature if they’re following a safety car or if there is a full course yellow, but normally [the brakes] warm up fairly easily, within the 1st lap. We also have a lot of tuning in terms of blanking panels for the air that feeds to cool them so there’s quite a lot we can do.’

Tyres

Running the low downforce configuration, particularly at Spa could lead to lower tyre grip, consequent slippage and therefore wear and degradation. However, this doesn’t seem to have been an issue so far with the Rebellion R13. ‘We haven’t really seen much tyre degradation at all, we’re happy with it in terms of suiting to our car,’ says Hayden. ‘We’re expecting to triple stint the tyres.’

Rebellion want to add the overall LMP1 Le Mans trophy to their cabinet but can their R13 beat Le Mans and then Toyota?

‘The main motivator for Rebellion to come back into P1 is not to win the championship, it is to win Le Mans,’ says team owner Bart Hayden. ‘You have a car that looks similar to the ORECA 07 P2 car, but it generates more downforce for less drag, weighs 100kg less, has got 60 to 70bhp more than the P2, in Le Mans trim, so it should be pretty handy, but I am not sure that it is handy enough to keep up with the Toyota.’

Deputy Editor of Racecar Engineering. Gemma is a qualified Engineer with a BEng in Mechanical Engineering from Bath University and an MSc in Advanced Motorsport Engineering from Cranfield University. She has worked trackside in BTCC and GT, reaching the F1 pitlane at the age of 23 as a Tyre Engineer for Pirelli. She then moved to Manor F1 as the team's Tyre and Strategy Engineer. In terms of writing, Hatton has been contributing to Racecar since she was 18, with her Motorsport experience helping to bring 'behind the scenes' tech to the Racecar pages. Proud of her geeky passion for all things Motorsport and Engineering, keep up to date with her tech talk on Twitter at @RacecarEngineer

FREE RACECAR ENGINEERING MONTHLY NEWSLETTER

About Us

Racecar Engineering is the world’s leading publication for motorsport technology and engineering. Every issue provides unrivalled technical analysis of everything from World Championship series including Formula 1, to grass roots racing. Using the expertise of industry professionals, we look in detail at racecar design and innovation, whilst also keeping you up to date with news and developments from all the major race series across the globe.